Testosterone is a potent androgenic hormone, produced chiefly by testes and occurs naturally in human body. It is responsible for the development of male reproductive organs and secondary sexual characteristics. It is an anabolic agent and its use may result in a significant increase in muscle mass, mood change (aggression), hair loss, deepened voice, acne and infertility. Anabolic steroids (of which testosterone is one) have been taken to enhance muscle development, strength, or endurance. They do so directly by increasing the muscles' protein synthesis.

Epitestosterone, on the other hand, is a chemically similar, natural steroid that is produced independently of testosterone because through a different bio-synthetic pathway.

The normal Testosterone (T) to Epitestosterone (E) ratio in urine varies from individual to individual and on average is one to one (1:1). This ratio does not vary significantly within an individual unless a testosterone or related preparation is consumed or injected or if some pathological condition exists. In such cases, the testosterone level can increase but epitestosterone levels tend to remain unaffected.

The T/E ratio greater than 4:1 in the urine of a person indicates steroid abuse unless there is evidence to the contrary i.e. unless there is convincing evidence that this ratio is due to a physiological or pathological condition. In case the T/E ratio is found to be greater than 4:1, it is mandatory for relevant medical authorities to conduct an investigation before the sample is declared positive.

A wide range of diagnostic tests have been developed to determine the testosterone to epitestosterone ratio in athletes who are accused of doping. Administration of epitestosterone is frequently done to mask a high level of testosterone if the standard T/E ratio test is used. As such, epitestosterone is banned by many sporting authorities being a well known masking agent for testosterone.

A T/E ratio higher than 6:1 was used to be considered as proof of abuse in the past; however, cases of naturally occurring higher T/E ratios have been described. Since the introduction of the T/E ratio in doping analysis, the parameters that may or may not influence the T/E ratio, possibly leading to false-positive results, have been debated.

Testosterone doping is detected by measuring the T/E ratios by gas chromatography/mass spectrometry according to the guidelines of the International Olympic Committee. Measurement of the ratio of testosterone (T) and epitestosterone (E) in urine has been used as an indication of ?natural? steroid supplementation for over a decade. The direct measurement of the glucuronide and sulfate conjugates of testosterone and epitestosterone by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS) has been proposed recently & is expected to resolve a number of issues regarding unusual metabolism due to either genetic disposition or attempts to avoid detection of abuse.